Irrigation control system

ABSTRACT

A tensiometer for use in determining matric potential of a soil comprising: a water inlet; a hydraulic coupler comprising a porous material for providing hydraulic coupling between water that enters the inlet and the soil; and a septum that seals water that enters the inlet against ingress of air via the porous material.

RELATED APPLICATIONS

The present application claims the benefit under 35 U.S.C. 119(e) ofU.S. Provisional Application 60/935,571 filed Aug. 20, 2007, thedisclosure of which is incorporated herein by reference.

FIELD

The invention relates to systems and apparatus for controllingirrigation systems.

BACKGROUND OF THE INVENTION

Irrigation systems that deliver water, often containing plant nutrients,pesticides and/or medications, to plants via networks of irrigationpipes are very well known. In some irrigation systems, externalsprinklers, emitters or drippers, are connected to the irrigation pipesto divert water from the pipes and deliver the water to plants. In manysuch irrigation networks, water from the pipes is delivered to theplants by emitters or drippers that are installed on or “integrated”inside the irrigation pipes. For convenience, any of the various typesof devices used in an irrigation system to divert water from anirrigation pipe in the system and deliver the diverted water to theplants is generically referred to as an emitter. Spacing betweenemitters, and emitter characteristics are often configured to respond todifferent irrigation needs of plants that the irrigation system is usedto irrigate.

For a given configuration of irrigation pipes and emitters, quantitiesof water delivered by the irrigation system may be controlled bycontrolling any of various water flow control devices, such as waterpumps, flow valves and check valves, and/or combinations of flow controldevices known in the art. Flow control devices may operate to controlwater from a source that provides water to all of, or a portion of,irrigation pipes in an irrigation system or to control water fromindividual emitters in the irrigation system.

Israel Patent Application 177552 entitled “Irrigation Pipe” filed Aug.17, 2006, the disclosure of which is incorporated herein by reference,describes an irrigation system having irrigation pipes comprisingintegrated emitters having different pressure thresholds at which theyopen to deliver water from the pipes. Which emitters open to deliverwater, is controlled by changing pressure in the irrigation pipes. U.S.Pat. No. 5,113,888, “Pneumatic Moisture Sensitive Valve”, the disclosureof which is incorporated herein by reference, describes a spray devicehaving its own valve that is opened and closed to control amounts ofwater that the device sprays on plants.

Various automatic and/or manual methods and systems are used todetermine when and how much water to supply to plants irrigated by anirrigation system and to control water flow devices in the systemaccordingly. U.S. Pat. No. 5,113,888 noted above, controls the waterflow valve in the spray device described in the patent responsive tosoil moisture. The spray device comprises an element located in the soilthat has pores, which are blocked when soil water moisture is above apredetermined amount and that are open when soil moisture is below apredetermined amount. When the pores are open, air is released from achamber in the valve relieving pressure that keeps the flow valve closedto allow the valve to open and water to flow to and be sprayed from thespray device. U.S. Pat. No. 6,978,794, the disclosure of which isincorporated herein by reference, describes controlling an irrigationsystem responsive to soil moisture determined by at least one timedomain reflectometry sensor (“TDRS”) located in the soil. The patentdescribes using multiple TDRS's at a different soil depth to providemeasurements of soil moisture content. U.S. Pat. No. 6,314,340, thedisclosure of which is incorporated herein by reference, describescontrolling water responsive to diurnal high and low temperatures.

For many agricultural and scientific applications, soil water matricpotential is used as a measure of soil moisture content and suitabilityof soil conditions for plant growth and irrigation systems are oftencontrolled responsive to measurements of soil matric potential. Watermatric potential, conventionally represented by “ψ”, is a measure of howstrongly particulate soil matter attracts water to adhere to theparticulate surfaces. The drier a soil, the stronger are the forces withwhich soil particles attract and hold water to their surfaces and thegreater is the water matric potential. As matric potential of a soilincreases, the more difficult it is for plants to extract water from thesoil. When soil gets so dry that plants cannot extract water from thesoil, plant transpiration stops and plants wilt.

Matric potential has units of pressure, is typically negative, and isconventionally measured using a tensiometer. A tensiometer usuallycomprises a porous material that is connected by an airtight seal to asealed reservoir filled with water. The porous material is placed incontact with soil whose matric potential, and thereby moisture content,is to be determined and functions to couple the reservoir to the soil toallow water but not air to pass between the reservoir and soil. Theforces that attract water to soil particles draw water through theporous material from the reservoir and generate a vacuum in thereservoir. The drier the soil, the greater are the forces that drawwater from the reservoir through the porous material and the greater isthe vacuum, i.e. the pressure of the vacuum decreases. As soil moistureincreases, the forces that attract water to the soil particles decreaseand water is drawn from the soil through the porous material into thereservoir and pressure of the vacuum increases. The vacuum increases(pressure decreases) or decreases (pressure increases) as water contentof the soil respectively decreases or increases. A suitable pressuremonitor is used to determine pressure of the vacuum and thereby providea measure of the soil matric potential.

The porous material in a tensiometer is usually a ceramic and is oftenformed having a cuplike or test tube-like shape. However, U.S. Pat. No.4,068,525, the disclosure of which is incorporated herein by reference,notes that the porous material “may be formed from any of a wide varietyof materials, including ceramics, the only requirement being that the‘bubbling pressure’, the pressure below which air will not pass throughthe wettened pores of the material, must be greater than normalatmospheric pressure, to prevent bubbles of air from entering theinstrument”. It is noted that bubbling pressure is generally maintainedonly when the porous material is saturated with water.

Additionally, the porous material should provide good hydraulic contactbetween the soils and the water reservoir. The latter constraint withrespect to soil contact generally requires that the porous material bein relatively intimate mechanical contact with soil particles. Whereassuch contact can usually be provided by a surface of a ceramic, forcoarse soils or gravels, such mechanical and resulting hydraulic contactcan be difficult to obtain using a ceramic material. Gee et al, in anarticle entitled “A Wick Tensiometer to Measure Low Tensions in CoarseSoils”; Soil Sci Soc. Am. J. 54:1498-1500 (1990) describes a tensiometerfor use in coarse soils in which the porous material “is constructedfrom paper toweling or other comparable wicking material rolled tightlyinto a cylinder (˜0.7 cm in diameter and ˜7 cm long).” The authors notethat the tightly rolled wicking material when wetted was pressure testedfor suitable bubbling pressure.

U.S. Pat. No. 5,156,179, the disclosure of which is incorporated hereinby reference, describes an irrigation system that is controlled using atensiometer responsive to water matric potential. The system comprises a“flow controller device” that includes a valve assembly connected withthe tensiometer to “provide automatic control of flow of water forirrigation”. Changes in pressure in the tensiometer move a piston in thevalve to provide “variable control of the rate of flow” through thevalve assembly “according to the matric tension of the soil for water”.

SUMMARY OF THE INVENTION

An aspect of some embodiments of the invention relates to providing atensiometer for measuring matric potential of a soil, for whichfunctions of providing hydraulic contact with the soil and sealing awater reservoir used with or comprised in the tensiometer againstingress of air through the hydraulic contact are provided by differentcomponents of the tensiometer.

According to an aspect of some embodiments of the invention, a septum,hereinafter a “sealing septum” interfaces the tensiometer waterreservoir with a component of the tensiometer formed from a porousmaterial that provides hydraulic contact between the tensiometerreservoir and the soil and when wet substantially seals the reservoiragainst ingress of air through the porous material. For convenience ofpresentation, the component formed from the porous material is referredto as a “hydraulic coupler”.

In an embodiment of the invention, because the sealing septumsubstantially provides appropriate sealing of the water reservoir, theporous material of the hydraulic coupler is generally not required whenwet to have a bubbling pressure greater than an absolute value of aminimum matric potential of the soil in which the tensiometer is to beused. (As noted above, matric potential is usually a negative pressure,and a minimum matric potential is negative pressure having a greatestabsolute value. Bubbling pressure of a material is the negative of aminimum matric potential at which air will not pass through thematerial, generally when the material is properly wetted.) Bysubstantially separating the function of providing hydraulic contactwith a soil and the function of sealing against passage of air, arelatively broad spectrum of materials can be used for the hydrauliccoupler and a tensiometer can advantageously be configured for specificagricultural applications while also providing relatively improvedhydraulic contact with the soil.

For example, according to an aspect of some embodiments of theinvention, the hydraulic coupler comprises a porous material in whichplant roots are able relatively easily to grow. Optionally, the porousmaterial comprises a woven and/or non-woven geotextile and/orfiberglass. Practice of the invention is not however, limited to suchmaterials and a tensiometer in accordance with an embodiment of theinvention may, for example, comprise any hydrophilic materialcharacterized by suitable porosity and may of course comprise relativelyrigid materials such as ceramics.

It is noted that the roots of many plants are able to generate hydraulicpressure equivalent to about 15 atmospheres in order to extract waterfrom soil. Such pressure can cause relatively steep gradients in soilmoisture for which soil in a near neighborhood of a plant's roots issubstantially drier than soil outside of the near neighborhood. Sinceplant growth and health are generally relatively sensitive to the soilenvironment near to their roots, a tensiometer for which plant roots areable to grow inside the tensiometer's hydraulic coupler can providewater matric potential measurements advantageously sensitive to soilconditions in the near neighborhoods of plant roots. Such measurementscan be particularly advantageous for use in controlling an irrigationsystem that provides water to the plants.

An aspect of some embodiments of the invention relates to providing atensiometer that is relatively inexpensive and simple to make and use.

In an embodiment of the invention, a tensiometer comprises a housinghaving a first housing part formed having an inlet orifice forcommunication with a sealed water reservoir and a second housing partformed to mate with the first part. The mated parts are assembledsandwiching a sealing septum between the orifice and a first region of aporous hydraulic coupling material that is located in the tensiometerhousing when the tensiometer is assembled. A second region of thehydraulic coupling material is located outside of the assembled housingand provides hydraulic coupling of the tensiometer to soil for which thetensiometer provides matric potential measurements. Optionally the firstand second housing parts are formed by injection molding plastic.Optionally, the sealing septum is formed from materials readilyavailable in the market such as a plastic, ceramic, or sintered metalcharacterized by a porosity having suitable uniformity and pore size.Optionally, the pore size has a characteristic dimension having anaverage between about 0.5 micron and about 1 micron. Optionally, thehydraulic coupling material comprises a geotextile. The tensiometer mayrapidly be assembled by any of various methods known in the art, such asby ultrasonic welding, gluing, or snap locking the first and secondhousing parts together.

An aspect of some embodiments of the invention, relates to providing aconfiguration of tensiometers that provides a measurement of watermatric potential responsive to water matric potential conditions over arelatively large area.

According to an aspect of some embodiments of the invention, a pluralityof tensiometers is distributed over the area and the tensiometers in theplurality are coupled to a same common water reservoir. Pressure of apartial vacuum in the common reservoir is responsive to the water matricpotential at each of the locations at which a tensiometer of theplurality of tensiometers is located. At equilibrium, pressure of apartial vacuum in the common water reservoir provides a measure,hereinafter a “representative matric potential”, of water matricpotential in the area that is intermediate a highest and lowest valuefor water matric potential provided by the tensiometers. A suitablepressure or vacuum gauge is used to provide a measurement of pressure inthe reservoir and thereby a measure of the representative matricpotential.

An aspect of some embodiments of the invention relates to providing animproved water management algorithm for controlling irrigation of afield responsive to water matric potential.

In an embodiment of the invention, an irrigation cycle defined by thealgorithm comprises a period of active irrigation during which thealgorithm controls an irrigation system to provide pulses of water to afield responsive to measurements of water matric potential in the field.Optionally, the cycle is a diurnal cycle. Optionally pulses of water areprovided responsive to comparing measurements of water matric potentialto a calibration water matric potential measurement. In an embodiment ofthe invention, the calibration water potential measurement is acquiredprior to the active irrigation period at a time for which plants in thefield have a relatively small demand for water. Generally, plantsexhibit a minimum in water demand at night, often in the early dawnhours and it is at such hours that calibration matric potentialmeasurements are, optionally, acquired. Optionally, the water matricpotential measurements are acquired using a tensiometer.

In an embodiment of the invention, an algorithm controls an irrigationsystem to provide water to a field continuously during an activeirrigation period. The duration of the active irrigation period isdetermined by the algorithm responsive to a comparison of a measurementof water matric potential for the field with a calibration water matricpotential.

There is therefore provided in accordance with an embodiment of theinvention, a tensiometer for use in determining matric potential of asoil comprising: a water inlet; a hydraulic coupler comprising a porousmaterial for providing hydraulic coupling between water that enters theinlet and the soil; and a septum that seals water that enters the inletagainst ingress of air via the porous material. Optionally, the porousmaterial comprises a geotextile. Additionally or alternatively, theporous material is adapted to enable growth of plant roots therein.

In some embodiments of the invention, the septum comprises a septumsurface, at least a part of which is contiguous with water that entersthe inlet. Optionally, the tensiometer comprises a water labyrinthhaving baffles. Optionally, a portion of the septum surface contacts thebaffles.

In some embodiments of the invention, the septum comprises a membraneand the septum surface is a surface of the membrane. Optionally, themembrane comprises a plurality of layers. Optionally, the layerscomprise a first layer having a bubbling pressure greater than about amaximum absolute value of the matric potential of the soil in which thetensiometer is used. Optionally, the first layer is supported by atleast one support layer. Optionally, the first layer is sandwichedbetween two support layers.

In some embodiments of the invention, the septum has a bubbling pressuregreater than about a maximum absolute value of the matric potential ofthe soil in which the tensiometer is used.

In some embodiments of the invention, the bubbling pressure is aboutequal to one atmosphere.

In some embodiments of the invention, a tensiometer comprises an elasticmember that resiliently presses the porous material to the septum.

In some embodiments of the invention, a tensiometer comprises a waterreservoir coupled to the water inlet.

In some embodiments of the invention, a tensiometer comprises a devicefor providing a measure of pressure in the water reservoir.

There is further provided in accordance with an embodiment of theinvention, an irrigation system comprising: an irrigation pipe having atleast one output orifice for outputting water from the pipe; at leastone tensiometer according to an embodiment of the invention coupled tothe irrigation pipe so that water output from an orifice of the at leastone orifice is constrained to pass substantially directly from theorifice through the hydraulic coupler. Optionally, the irrigation pipecomprises at least one emitter and an output orifice is an orifice ofthe at least one emitter. Additionally or alternatively, the at leastone emitter is an integrated emitter. Additionally or alternatively, theat least one emitter comprises a plurality of emitters.

In some embodiments of the invention, each of the at least onetensiometer is coupled to a same water reservoir.

There is further provided in accordance with an embodiment of theinvention, apparatus for use in determining matric potential of a soilcomprising: a plurality of tensiometers; and a same water reservoir towhich all the tensiometers are hydraulically coupled. Optionally, theplurality of tensiometers comprises a tensiometer in accordance with anembodiment of the invention. Additionally or alternatively, theapparatus comprises a valve adapted to connect the irrigation system toa water source and operable to enable water from the water source toenter the reservoir and remove air therefrom.

There is further provided in accordance with an embodiment of theinvention, an irrigation system comprising: an irrigation pipe having atleast one output orifice for outputting water from the pipe; at leastone tensiometer comprising a hydraulic coupler for coupling thetensiometer to soil irrigated by the irrigation system; and a valveadapted to connect the irrigation system to a water source and operableto enable water from the water source to enter the at least onetensiometer and flush air from the tensiometer and coupler.

There is further provided in accordance with an embodiment of theinvention, a tensiometer for use in determining matric potential of asoil comprising: a water inlet; a hydraulic coupler comprising a porousmaterial for providing hydraulic coupling between water that enters theinlet and the soil; a valve adapted to connect the tensiometer to awater source and operable to enable water from the water source to enterthe tensiometer and flush the hydraulic coupler.

There is further provided in accordance with an embodiment of theinvention, a method of irrigating a field, the method comprising:acquiring a calibration water matric potential for the field; andirrigating the field with an amount of water responsive to the value ofthe calibration matric potential. Optionally, irrigating a fieldcomprises performing an irrigation cyclically. Optionally, irrigatingthe field cyclically comprises irrigating the field in diurnal cycles.Optionally, acquiring a calibration water matric potential comprisesacquiring a calibration water matric potential at least once a day.

In some embodiments of the invention, the field comprises plants andacquiring the calibration water matric potential comprises acquiring thematric potential when the plants exhibit relatively small water demand.

In some embodiments of the invention, providing an amount of watercomprises providing a pulse of water. Optionally, providing an amount ofwater comprises acquiring a water matric potential measurement for thefield in addition to the calibration water matric potential, comparingthe additional water matric potential measurement to the calibrationwater matric potential, and providing an amount of water responsive tothe comparison. Optionally, comparing the additional water matric to thecalibration matric potential comprises determining their difference.Optionally, providing a pulse of water comprises providing the pulseresponsive to the difference.

In some embodiments of the invention, providing water comprisesproviding water continuously. Optionally, providing water continuously,comprises determining an irrigation period responsive to the calibrationwater matric potential and providing water continuously for thedetermined irrigation period. Optionally, determining the irrigationperiod comprises determining the irrigation period responsive to adifference between the calibration water matric and a previouslydetermined calibration water matric.

There is further provided in accordance with an embodiment of theinvention, an irrigation system comprising: an irrigation pipe having atleast one output orifice for outputting liquid from the pipe; at leastone hydraulic coupler coupled to the irrigation pipe so that liquidoutput from an orifice of the at least one orifice passes through thehydraulic coupler; and at least one sensing means coupled to thehydraulic coupler to sense a property associated with liquid in thehydraulic coupler, responsive to which property output of water via theat least one orifice is controlled. Optionally, the sensed propertycomprises matric potential. Additionally or alternatively, the sensedproperty comprises moisture content of the hydraulic coupler.

Optionally, the irrigation system comprises a controller that controlsoutput of water via the at least one orifice responsive to the sensedproperty.

BRIEF DESCRIPTION OF FIGURES

Non-limiting examples of embodiments of the invention are describedbelow with reference to figures attached hereto and listed below.Identical structures, elements or parts that appear in more than onefigure are generally labeled with a same numeral in all the figures inwhich they appear. Dimensions of components and features shown in thefigures are chosen for convenience and clarity of presentation and arenot necessarily shown to scale.

FIG. 1A schematically shows an exploded view of a tensiometer, inaccordance with an embodiment of the invention;

FIG. 1B schematically shows details of a top housing part of thetensiometer shown in FIG. 1A, in accordance with an embodiment of theinvention;

FIG. 1C schematically shows a plan view of the top housing part shown inFIG. 1B, in accordance with an embodiment of the invention;

FIG. 1D schematically shows a perspective view of a bottom housing partof the tensiometer shown in FIG. 1A, in accordance with an embodiment ofthe invention;

FIG. 2 schematically shows an assembled view of the tensiometer shown inFIGS. 1A-1B, in accordance with an embodiment of the invention;

FIG. 3 schematically shows a side cross-sectional view of thetensiometer shown in FIG. 1A and FIG. 2 connected to a sealed waterreservoir, in accordance with an embodiment of the invention;

FIG. 4 schematically shows a configuration of tensiometers distributedin the soil of an agricultural field in which plants are grown, inaccordance with an embodiment of the invention;

FIGS. 5A and 5B show a flow diagram of an algorithm for controllingirrigation of a field responsive to water matric potential in accordancewith an embodiment of the invention; and

FIG. 6 shows a flow diagram of another algorithm for controllingirrigation of a field responsive to water matric potential in accordancewith an embodiment of the invention.

DETAILED DESCRIPTION

FIG. 1A schematically shows an exploded view of a tensiometer 20 formeasuring water matric potential in a soil, in accordance with anembodiment of the invention. FIGS. 1B-1D schematically show enlargedviews of components of tensiometer 20 shown in FIG. 1A. FIG. 2schematically shows an assembled view of tensiometer 20. For convenienceof presentation, apparatus 20 is referred to as a tensiometer, eventhough, as shown in FIGS. 1A-1D, it optionally, does not comprise awater reservoir and apparatus for providing a measure of pressure in thereservoir.

Tensiometer 20 optionally comprises a housing 22 having first and secondhousing parts 30 and 50, hereinafter referred to for convenience ashousing top 30 and housing bottom 50, a sealing septum 60, a hydraulicsoil coupler 70 formed from a porous material and a resilient element80.

Hydraulic coupler 70 is formed having a soil-coupling region 72 thatextends outside of housing 22 when tensiometer 20 is assembled (FIG. 2)and is a part of tensiometer 20 that contacts soil for which thetensiometer provides water matric potential measurements andhydraulically couples the tensiometer to the soil. Optionallysoil-coupling region 72 enlarges with distance from tensiometer housing22. Hydraulic coupler 70 optionally comprises a neck region 74 and anoptionally circular reservoir-coupling region 76 that are discussedbelow and are located inside housing 22. Hydraulic coupler 70 isoptionally formed from a flexible porous material and is optionally suchthat plants that are to be grown in a soil for which tensiometer 20 isto be used to monitor water matric potential can intrude their roots.Optionally, hydraulic coupler 70 is formed from a material comprising ageotextile.

Housing top 30 comprises a tubular stem 31 having a lumen for connectingtensiometer 20 to a sealed tensiometer water reservoir and is formedhaving a septum recess 33, shown in a perspective view of first housingpart 30 from a side opposite that of stem 31 in FIG. 1B, that seatssealing septum 60. A bottom surface 34 of septum recess 33 is formedhaving an inlet hole 35, clearly shown in a plan view of housing top 30in FIG. 1C, through which water from a reservoir connected to stem 31enters tensiometer 20. Bottom surface 34 of septum recess 33 isoptionally formed having a water flow labyrinth 36 comprising anentrance, “detour” baffle 37 that covers portions of inlet hole 35 and aplurality of raised cylindrical baffles 38. Detour baffle 37 isoptionally “starfish shaped” comprising five angularly, equally spacedarms 39. Labyrinth 36 is surrounded by an annular, optionally planarsurface 40 devoid of labyrinth components. Housing top 30 optionallycomprises a neck 41 formed having a channel 42 for receiving neck region74 of hydraulic coupler 70 and optionally comprises an assembly ridge 44for mounting housing top 30 to housing bottom 50.

Sealing septum 60 optionally comprises a porous septum membrane 61supported by an annular septum frame 62, which optionally protrudes oneither side of the plane of the septum membrane. When tensiometer 20 isassembled, the annular septum frame seats on annular region 40 of bottomsurface 34 and septum membrane 61 optionally rests on and is supportedby detour and cylindrical baffles 37 and 38.

Septum membrane 61 transmits water but is characterized by a bubblingpressure, hereinafter referred to as an “operating bubbling pressure”,when wet that is equal to a maximum water matric potential, typicallybetween about −0.2 bar to about −0.7 bar, expected to be encountered ina soil in which tensiometer 20 is to be used. Optionally, the operatingbubbling pressure of porous membrane 61 is equal to about 1 atmosphere.As a result, water can pass through membrane 61 relatively easily, butfor a pressure differential across the membrane less than or equal toabout a maximum water matric potential of soil in which tensiometer 20is used, membrane 61 is substantially impervious to air. Optionally,membrane 61 is a layered structure, schematically shown in an inset 66in FIG. 1A, and optionally comprises a porous layer 63, which transmitswater but when wet is impervious to air for pressures less than anappropriate operating bubbling pressure, sandwiched between two supportlayers 64. Optionally, porous layer 63 is formed by way of example froma ceramic, and/or a sintered metal and/or a suitable woven or non-wovenfabric having suitable porosity. Support layers 64 are optionallymeshed, or screen-like layers formed from any suitably rigid and strongmaterial. Optionally, porous layer 63 is characterized by an averagepore size from about 0.5 to about 1 micron. Optionally, support layersare formed from a metal and/or plastic.

Housing bottom 50 is formed to mate with housing top 30 and isoptionally formed having a mating ridge 51 that is matched to fit insiderecess 33 (FIG. 1B) formed in housing top 30 so that it aligns thehousing top and bottom. Mating ridge 51 defines a portion of a boundaryof a recess 52 that seats reservoir-coupling region 76 (FIG. 1A) ofhydraulic coupler 70. The housing bottom also comprises a neck 54 formedhaving a channel 55 that matches neck 41 and channel 42 respectively ofhousing top 30. A bottom surface 56 of recess 52 is optionally formedhaving a cavity 57 for receiving resilient element 80, optionally in ashape of a sphere, formed from an elastic material. An outer, optionallyplanar peripheral border 58 surrounds mating ridge 51 and channel 55.

When tensiometer 20 is assembled, assembly ridge 44 of housing top 30contacts and is bonded to peripheral border 58 of housing bottom 50 andmating ridge 51 presses annular septum frame 62 to annular surface 40 ofhousing top 30 to secure septum 50 in septum recess 33 of the housingtop. Resilient sphere 80 is slightly compressed and urgesreservoir-coupling region of hydraulic coupler 70 to resiliently presson septum membrane 61 and the septum membrane to rest securely on waterlabyrinth baffles 37 and 38. Because of the secure contact betweenseptum membrane 61 and labyrinth baffles 37 and 38, water that enterstensiometer 20 is distributed substantially equally over the surface ofseptum membrane 61 that contacts the labyrinth baffles. Starfish detourbaffle 37 operates to direct substantially equal portions of water thatenters inlet hole 35 to flow radially in each of five different sectorsdefined by the starfish baffle arms 39. Cylindrical baffles 38 disperseradially flowing water azimuthally. As a result, water that enterstensiometer 20 through inlet hole 35 wets substantially equally allregions of septum membrane 61 and the membrane becomes substantiallyimpervious to passage of air for the bubbling pressure for which it isintended.

FIG. 3 schematically shows a side cross-sectional view of tensiometer 20shown in FIG. 1A and FIG. 2 connected to a sealed water reservoir 100partially filled with water 120 and being used to determine a value forthe water matric potential ψ of a soil region 130, in accordance with anembodiment of the invention. It is noted that whereas water reservoir100 is shown above the surface of soil region 130, in practice, thewater reservoir is generally located below the surface of soil for whichthe tensiometer is used to measure water matric potential.

Tensiometer 20 is positioned in soil region 130 so that soil-couplingregion 72 of hydraulic coupler 70 is in contact with soil in the soilregion. A pressure gauge 102 is coupled to water reservoir 100 tomeasure pressure in the reservoir. In FIG. 3, by way of example, thepressure gauge is shown as a manometer having a left hand branch 103coupled to water reservoir 100 and a right hand branch 104 exposed toatmospheric pressure. The manometer is assumed to comprise mercury 125as a manometer fluid, and left hand branch 103 between the mercury andwater 120 in reservoir 100 is filled with water. Whereas in FIG. 3pressure gauge 102 is shown as a manometer, in practice any suitablepressure gauge or sensor known in the art may be used to provide ameasure of pressure in reservoir 100.

Hydraulic coupler 70 provides a hydraulic coupling between soil in soilregion 130 and water in water reservoir 100 via contact betweenreservoir-coupling region 76 (FIG. 1A) of the hydraulic coupler andsealing septum 60. The soil draws water from or introduces water intowater reservoir 100 via the hydraulic coupler depending on whether thewater matric potential of soil region 130 is greater than or less thanthe pressure in water reservoir 100. Equilibrium is established forwhich there is substantially no water flow from or into the reservoirwhen pressure in the reservoir is equal to the soil water matricpotential. Since the matric potential is almost always negative, thereis a vacuum in reservoir 100 above a waterline 121 of water 120 in thereservoir. In FIG. 3 mercury 125, is higher in left hand branch 103 ofthe manometer connected to water reservoir 100 than in right hand branch104 of the manometer exposed to atmospheric pressure. A differencebetween the height of mercury in the left and right hand branchesprovides a measure of the partial vacuum in water reservoir 100 andthereby of the matric potential ψ.

In order to operate reliably, advantageously, septum membrane ismaintained properly wetted and does not have air trapped in its pores.However, during operation, air might leak through hydraulic coupler 70or seep through water 120 and be trapped by the membrane or in spacesbetween baffles 37 and 38 of labyrinth 39. In order to purge septum 61and/or labyrinth 36 of air that they may trap, a purge valve 105 isoptionally connected to reservoir 100. Purge valve 105 is connected to asuitable source of water (not shown) and in accordance with anembodiment of the invention is periodically opened to flush water fromthe water source through the reservoir, septum membrane 61, andlabyrinth 36 to purge the septum and labyrinth of air they may havetrapped. Advantageously, the space above waterline 121 is substantiallya vacuum and water provided via purge valve 105 is used to remove airfrom reservoir 100.

In an embodiment of the invention, to provide a measure of matricpotential ψ in a region of a field, a plurality of tensiometers,optionally of a type shown in FIGS. 1A-3, is positioned in soil atdifferent locations in the field and coupled to a common sealed waterreservoir. Pressure in the common water reservoir provides a measure,i.e. “representative matric potential”, of water matric potential in thefield that is intermediate a highest and lowest value for water matricpotential provided by the tensiometers. Optionally, the field is anagricultural field for growing plants and the plurality of tensiometersand representative matric potential is used to control irrigation of theplants in the field.

FIG. 4 schematically shows a configuration of tensiometers 200distributed in the soil of an agricultural field 240 in which plants 242are grown, in accordance with an embodiment of the invention. Thetensiometers are connected to a same water reservoir 202 connected to apressure gauge 204 used to provide a measure of a partial vacuum in thereservoir and thereby of a representative matric potential of the regionof agricultural field 240 in which the tensiometers are located.

By way of example, in FIG. 4 plants 242 are irrigated using anirrigation pipe 210, comprising integrated emitters 212 and tensiometers200 are of a type shown in FIGS. 1A-3 having hydraulic couplers 70formed from a geotextile in which roots 244 of plants 242 are able togrow. In accordance with an embodiment of the invention, eachtensiometer 200 coupled to water reservoir 202 is located in aneighborhood of a plant 242 and has its hydraulic coupler 70 wrappedaround a region of irrigation pipe 210 in which an emitter 212 islocated. Some roots 244 of plants 242 are shown growing into thegeotextile fabric of hydraulic couplers 70 of tensiometers 200. Becauseof the close proximity of emitters 212 and plant roots 244 to hydrauliccouplers 70, each tensiometer 200 is responsive to soil water matricpotential to which plants 242 are relatively sensitive and to changes inthe matric potential produced by water emitted by emitters 212.

In an embodiment of the invention, measurements of changes in pressurein reservoir 202, and thereby of changes in representative water matricpotential of field 240, provided by pressure gauge 204 are used tocontrol water emitted by emitters 212. When the representative watermatric potential provided by pressure gauge 204 falls below a desiredlower threshold for water matric potential, emitters 212 are controlledto release water to the soil. When the representative water matricpotential rises above a desired upper threshold, the emitters areprevented from delivering water to the soil.

Optionally, emitters 212 release water to soil region 240 only afterpressure in irrigation pipe 210 rises above a release water thresholdpressure and water released by emitters 212 is controlled by controllingpressure in the irrigation pipe. In some embodiments of the invention,water release is controlled by pulsing pressure in irrigation pipe 210above the emitter threshold pressure. In some embodiments of theinvention, pressure pulses are periodic and are characterized by a pulselength. The period and pulse length of the pressure pulse are optionallydetermined responsive to a “hydration” relaxation time of soil in soilregion 240 characteristic of a time it takes the soil to reach alimiting water matric potential following release of a quantity of waterto the soil by an emitter 212 during a pressure pulse. Controllingrelease of water in accordance with an embodiment of the invention bypulsing water pressure responsive to a soil hydration relaxation timecan be advantageous in providing relatively accurate control ofirrigation. For example, it can be advantageous in preventing overirrigation of plants 242.

The inventors of embodiments of the invention have carried outirrigation experiments in which plants were irrigated responsive to arepresentative matric potential in accordance with an embodiment of theinvention. The inventors found that they were able to achieve relativelyimproved crop yields with relatively smaller quantities of water thanwould normally be provided to the plants.

Under some conditions, a representative water matric potential providedby a plurality of tensiometers in accordance with an embodiment of theinvention is substantially equal to an average of the measurementsprovided by the tensiometers. For example, assume that at a location ofan “i-th” tensiometer 200, for convenience represented by “T_(i)”, insoil region 240, the water matric potential is ψ_(i). At equilibrium, apartial vacuum in water reservoir 202 settles down to a pressure equalto that of a representative matric potential “ψ_(o)”. At therepresentative matric potential, as much water enters water reservoir202 from tensiometers T_(i) at locations for which matric potentialsψ_(i)>ψ_(o) as exits the water reservoir from tensiometers T_(i) atlocations for which ψ_(i)<ψ_(o). Assume that water flow into or out of atensiometer T_(i) is proportional to (ψ_(i)−ψ_(o))/R where R is aresistance to water transport of soil in soil region 240, which is thesame for all locations of tensiometers T_(i), and is independent of(ψ_(i)−ψ_(o)). Then at equilibrium,

${{\sum\limits_{i}^{N}{\left( {{\Psi \; i} - {\Psi \; o}} \right)\text{/}R}} = {{0\mspace{14mu} {and}\mspace{14mu} \psi_{o}} = {\left( {1\text{/}N} \right){\sum\limits_{i}^{N}{\Psi i}}}}},$

so that ψ_(o) is an average of all the ψ_(i). However, it is expectedthat, in general, R will not only not be the same for all locations ofsoil region 130 but will be dependent on (ψ_(i)−ψ_(o)). As a result, itis expected that a given representative water matric potential will ingeneral be some sort of weighted average of the matric potential at thelocations of each of tensiometers 200.

In some embodiments of the invention, provision of water to anagricultural field by an irrigation system, such as agricultural field240 and the irrigation system shown in FIG. 4, which providesmeasurements of soil water matric potential ψ is controlled inaccordance with an algorithm 300 having a flow diagram similar to thatshown in FIGS. 5A and 5B. The flow diagram delineates an optionallydiurnal water provision cycle in which the irrigation system providespulses of water to the field subject to certain “trigger” conditions,described below, prevailing.

In a block 301, optionally values for parameters that control the waterprovision cycle T_(cal), T_(diff), T_(B) and T_(E) are determined.T_(cal) is a time during the diurnal cycle at which the irrigationsystem calibrates water matric potential measurements and acquires acalibration water matric potential measurement M_(o). M_(o) isoptionally acquired during night after a period of time during whichirrigation was not provided and water demand by plants in the field isminimal. Optionally, T_(cal) is about 0500. T_(diff) is an optionallyfixed, maximum time lapse allowed by algorithm 300 between provision ofpulses of water to field 240. Optionally, T_(diff) is equal to about 5hours. T_(B) is a time following time T_(cal) at which the irrigationsystem begins a period of “active irrigation” in which it provides apulse of water to field 240 when a trigger condition occurs. T_(E) is atime at which the active irrigation period ends. Optionally, T_(B) isabout an hour later than T_(cal) and T_(E) is a time at about dusk, forexample about 1700.

In a step 302, algorithm 300 checks a system clock (not shown) toacquire a reading of the time, “T_(clock)”. In a decision block 303 thetime T_(clock) is checked to see if it is about equal to T_(cal). If itis not, then the algorithm returns to block 302 to acquire a new readingfor T_(clock). If on the other hand T_(clock) is about equal to T_(cal),algorithm 300 advances to a block 304 and acquires a calibrationreading, M_(o), of the soil matric potential ψ. The algorithm thenproceeds to acquire another reading, T_(clock), of the system clock in ablock 305 and then proceeds to a decision block 306. In decision block306 algorithm 300 determines if T_(clock) is greater than or equal totime T_(B) at which active irrigation of field 240 is to commence. IfT_(clock) is less than T_(B), the algorithm returns to block 305 toacquire another reading for T_(clock). If on the other hand T_(clock) isgreater than or about equal to T_(B), algorithm 300 advances to a block307 and sets a variable time parameter T_(P) equal to T_(clock), and ina block 308 optionally sets ΔT equal to (T_(clock)−T_(P)), whichinitializes ΔT to zero.

Optionally, in a decision block 309, algorithm 300 determines if ΔT isgreater than T_(diff). If it is not, (which at this stage, immediatelyafter initialization, is the case) algorithm 300 optionally skips to ablock 313. In block 313 algorithm 300 acquires a measurement M_(I) ofthe water matric potential of field 240, optionally responsive toreadings from tensiometers 200 (FIG. 4), and proceeds to determine in adecision block 314 if the absolute value of |M_(I)| is greater than theabsolute value |M_(o)| acquired in block 304. If |M_(I)| is greater than|M_(o)|, algorithm 300 optionally proceeds to a block 315 and controlsthe irrigation system to provide a pulse of water to field 240.

In some embodiments of the invention, a pulse of water provided by theirrigation system is determined to provide about 0.6 liters of water perm² of field 240. The inventors have determined that aforementionedamount of water per pulse is convenient to maintain appropriateirrigation, generally, if a time between pulses is greater than or aboutequal to 0.5 hours. In some embodiments of the invention, algorithm 300increases an amount of water provided by an irrigation pulse if timebetween pulses decreases to less than about 0.5 hours. For example, ifirrigation algorithm 300 “finds” that |M_(I)| increases relativelyrapidly, indicating a requirement for irrigation pulses every 0.25hours, optionally the algorithm increases the mount of water provided byan irrigation pulse. Optionally, the algorithm increases water providedby a pulse to about 0.9 liters/m² if it finds that demand for irrigationpulses reaches a rate of about 4 pulses per hour.

Following provision of the pulse of water, algorithm 300 proceeds to ablock 316 and acquires a new reading for T_(clock) and resets T_(P) toT_(clock) in a block 317. It is noted that in decision block 314, if|M_(I)| is less than |M_(o)|, algorithm 300 skips blocks 315 to 317,does not provide a pulse of water, and goes directly to a decision block318 shown in FIG. 5B.

Returning to block 309 if ΔT is greater than T_(diff), algorithm 300does not skip to block 314 where it measures M_(I), but rather,optionally, proceeds to a block 310 and provides a pulse of irrigatingwater to field 240. Thereafter the algorithm proceeds to a block 311,acquires a new reading for T_(clock), and in a block 312 resets T_(P) toT_(clock). It then proceeds to block 314 to measure M_(I) and via blocks315-317 eventually to decision block 318.

In decision block 318 algorithm 300 determines if T_(clock) is greaterthan or equal to T_(E), the time set in block 301 at which the activeirrigation period ends and a new irrigation cycle begins. If T_(clock)is less than T_(E), algorithm 300 returns to block 308 and resets ΔT,otherwise, the algorithm returns to block 302 to begin the cycle again.

In some embodiments of the invention, an agricultural field, such asfield 240 (FIG. 4) is irrigated in accordance with an algorithm 400having a flow diagram shown in FIG. 6. Algorithm 400 controls anirrigation system to continuously provide water to agricultural field240 during an active irrigation period instead of by pulsing waterprovision.

In a block 401 of algorithm 400, optionally parameters T_(B), T_(E),T_(diff), T_(irr), T_(cal), and M_(diff) are set. As in algorithm 300,T_(B) and T_(E) are begin and end times of active irrigation and T_(cal)is a calibration time. T_(irr) is an initial value for duration of theactive irrigation period, and T_(diff) is an adjustment to T_(irr),which algorithm 400 makes subject to certain water matric potentialconditions of field 240. M_(diff) is an optionally fixed, maximum changein water matric potential for which algorithm 400 does not adjustT_(irr). Affects of the parameters set in block 401 on decisions ofalgorithm 400 are clarified below. In some embodiments of the invention,T_(irr) and T_(diff) have values equal to about 3 hours and 0.2 hours,respectively. M_(diff) is optionally a positive number having valueequal to a fraction less than one of a typical matric potential for thefield being irrigated with the irrigation system. Optionally, M_(diff)is equal to about 5% of a calibration matric potential acquired for thefield. Optionally, for a given day, M_(diff) is equal to 5% of acalibration matric potential for a previous day.

In a block 402, algorithm 400 acquires a value for T_(clock), andoptionally in a decision block 403 determines if T_(clock) is equal toT_(cal). If it is not it returns to block 402 to acquire a new value forT_(clock). On the other hand, if T_(clock) is equal to T_(cal) thealgorithm proceeds to a block 404 and acquires a reading “M_(n)” for thewater matric potential ψ of field 240. The subscript “n” refers to an“n-th” day, assumed a current day, of operation of the irrigation systemin providing water to field 240. In a block 404, algorithm 400 storesthe value for M_(n) in a suitable memory. In a block 405 the algorithmoptionally assigns a value to ΔM equal to a difference between of thecurrent reading M_(n) of the water matric potential and a value of areading, M_(n-1), of the water matric potential acquired for the daybefore the current day.

In a decision block 406, algorithm 400 determines if an absolute valueof ΔM is greater than or equal to M_(diff). If it is, the algorithmproceeds to a decision block 407 to determine if ΔM is greater than orequal to zero. If ΔM is greater than zero, the algorithm proceeds fromblock 407 to a block 408 where it decreases T_(irr) by an amountT_(diff) and then proceeds to a block 410 to acquire time T_(clock). IfΔM is less than zero, the algorithm proceeds from block 407 to a block409 where it increases T_(irr) by an amount T_(diff) and then proceedsto a block 410 to acquire time T_(clock).

If in decision block 406 the absolute value of ΔM is less than M_(diff),then algorithm 400 skips directly from block 406 to block 410 to acquireT_(clock), skipping blocks 407, 408 and 409.

From block 410, the algorithm proceeds to decision block 411. Indecision block 411, algorithm 400 determines if T_(clock) acquired inblock 410 is greater than or equal to the active irrigation begin timeT_(B). If it is not, it returns to block 410 to acquire a new value forT_(clock) and then to block 411 to test the new T_(clock). If in block411 the algorithm determines that T_(clock) is greater than or equal toT_(B), the algorithm proceeds to a block 412 and begins continuousirrigation of field 240.

From block 412 the algorithm continues to a block 413 to acquire a newvalue for T_(clock) and in a decision block 414 determines if(T_(clock)−T_(B)) is greater than or equal to T_(irr). If it is not, thealgorithm returns to block 412 to continue continuous irrigation offield 240. If on the other hand, (T_(clock)−T_(B))>T_(irr) then thealgorithm ends continuous irrigation and returns to block 403.

In the description and claims of the present application, each of theverbs, “comprise” “include” and “have”, and conjugates thereof, are usedto indicate that the object or objects of the verb are not necessarily acomplete listing of members, components, elements or parts of thesubject or subjects of the verb.

The invention has been described with reference to embodiments thereofthat are provided by way of example and are not intended to limit thescope of the invention. The described embodiments comprise differentfeatures, not all of which are required in all embodiments of theinvention. Some embodiments of the invention utilize only some of thefeatures or possible combinations of the features. Variations ofembodiments of the described invention and embodiments of the inventioncomprising different combinations of features than those noted in thedescribed embodiments will occur to persons of the art. The scope of theinvention is limited only by the following claims.

1. A tensiometer for use in determining matric potential of a soilcomprising: a water inlet; a hydraulic coupler comprising a porousmaterial for providing hydraulic coupling between water that enters theinlet and the soil; and a septum that seals water that enters the inletagainst ingress of air via the porous material.
 2. A tensiometeraccording to claim 1 wherein the porous material comprises a geotextile.3. A tensiometer according to claim 1 wherein the porous material isadapted to enable growth of plant roots therein.
 4. A tensiometeraccording to claim 1 wherein the septum comprises a septum surface, atleast a part of which is contiguous with water that enters the inlet. 5.A tensiometer according to claim 4 wherein the tensiometer comprises awater labyrinth having baffles.
 6. A tensiometer according to claim 5wherein a portion of the septum surface contacts the baffles.
 7. Atensiometer according to claim 4 wherein the septum comprises a membraneand the septum surface is a surface of the membrane.
 8. A tensiometeraccording to claim 7 wherein the membrane comprises a plurality oflayers.
 9. A tensiometer according to claim 8 wherein the layerscomprise a first layer having a bubbling pressure greater than about amaximum absolute value of the matric potential of the soil in which thetensiometer is used.
 10. A tensiometer according to claim 9 wherein thefirst layer is supported by at least one support layer.
 11. Atensiometer according to claim 10 wherein the first layer is sandwichedbetween two support layers.
 12. A tensiometer according to claim 1wherein the septum has a bubbling pressure greater than about a maximumabsolute value of the matric potential of the soil in which thetensiometer is used.
 13. A tensiometer according to claim 9 wherein thebubbling pressure is about equal to one atmosphere.
 14. A tensiometeraccording to claim 1 comprising an elastic member that resilientlypresses the porous material to the septum.
 15. A tensiometer accordingto claim 1 and comprising a water reservoir coupled to the water inlet.16. A tensiometer according to claim 1 and comprising a device forproviding a measure of pressure in the water reservoir.
 17. Anirrigation system comprising: an irrigation pipe having at least oneoutput orifice for outputting water from the pipe; at least onetensiometer according to claim 1 coupled to the irrigation pipe so thatwater output from an orifice of the at least one orifice is constrainedto pass substantially directly from the orifice through the hydrauliccoupler.
 18. An irrigation system according to claim 17 wherein theirrigation pipe comprises at least one emitter and an output orifice isan orifice of the at least one emitter.
 19. An irrigation systemaccording to claim 17 wherein the at least one emitter is an integratedemitter.
 20. An irrigation system according to claim 18 wherein the atleast one emitter comprises a plurality of emitters.
 21. An irrigationsystem according to claim 17 wherein each of the at least onetensiometer is coupled to a same water reservoir.
 22. Apparatus for usein determining matric potential of a soil comprising: a plurality oftensiometers; and a same water reservoir to which all the tensiometersare hydraulically coupled.
 23. Apparatus for use in determining matricpotential of a soil comprising: A tensiometer according to claim 1; anda same water reservoir to which all the tensiometers are hydraulicallycoupled.
 24. Apparatus according to claim 22 and comprising a valveadapted to connect the irrigation system to a water source and operableto enable water from the water source to enter the reservoir and removeair therefrom.
 25. An irrigation system comprising: an irrigation pipehaving at least one output orifice for outputting water from the pipe;at least one tensiometer comprising a hydraulic coupler for coupling thetensiometer to soil irrigated by the irrigation system; and a valveadapted to connect the irrigation system to a water source and operableto enable water from the water source to enter the at least onetensiometer and flush air from the tensiometer and coupler.
 26. Atensiometer for use in determining matric potential of a soilcomprising: a water inlet; a hydraulic coupler comprising a porousmaterial for providing hydraulic coupling between water that enters theinlet and the soil; and a valve adapted to connect the tensiometer to awater source and operable to enable water from the water source to enterthe tensiometer and flush the hydraulic coupler.
 27. A method ofirrigating a field, the method comprising: acquiring a calibration watermatric potential for the field; and irrigating the field with an amountof water responsive to the value of the calibration matric potential.28. A method according to claim 28 wherein irrigating a field comprisesperforming an irrigation cyclically.
 29. A method according to claim 28wherein irrigating the field cyclically comprises irrigating the fieldin diurnal cycles.
 30. A method according to claim 29 wherein acquiringa calibration water matric potential comprises acquiring a calibrationwater matric potential at least once a day.
 31. A method according toclaim 27 wherein the field comprises plants and acquiring thecalibration water matric potential comprises acquiring the matricpotential when the plants exhibit relatively small water demand.
 32. Amethod according to claim 27 wherein irrigating the field with an amountof water comprises providing a pulse of water.
 33. A method according toclaim 32 wherein providing an amount of water comprises acquiring awater matric potential measurement for the field in addition to thecalibration water matric potential, comparing the additional watermatric potential measurement to the calibration water matric potential,and irrigating the field with an amount of water responsive to thecomparison.
 34. A method according to claim 33 wherein comparing theadditional water matric to the calibration matric potential comprisesdetermining their difference.
 35. A method according to claim 34 whereinproviding a pulse of water comprises providing the pulse responsive tothe difference.
 36. A method according to claim 27 wherein providingwater comprises providing water continuously.
 37. A method according toclaim 36 wherein providing water continuously, comprises determining anirrigation period responsive to the calibration water matric potentialand providing water continuously for the determined irrigation period.38. A method according to claim 37 wherein determining the irrigationperiod comprises determining the irrigation period responsive to adifference between the calibration water matric and a previouslydetermined calibration water matric.
 39. An irrigation systemcomprising: an irrigation pipe having at least one output orifice foroutputting liquid from the pipe; at least one hydraulic coupler coupledto the irrigation pipe so that liquid output from an orifice of the atleast one orifice passes through the hydraulic coupler; and at least onesensing means coupled to the hydraulic coupler to sense a propertyassociated with liquid in the hydraulic coupler, responsive to whichproperty output of water via the at least one orifice is controlled. 40.An irrigation system according to claim 39 wherein the sensed propertycomprises matric potential.
 41. An irrigation system according to claim39 wherein the sensed property comprises moisture content of thehydraulic coupler.
 42. An irrigation system according to claim 39comprising a controller that controls output of water via the at leastone orifice responsive to the sensed property.